As semiconductor devices have become more highly integrated, the wafer feature dimensions and depth profile have been reduced to below the subhalf micron level. To achieve high device reliability and low defect rates, it is essential to maintain an ultraclean environment on the wafer. This requirement has placed a demand for higher gas system performance which in return demands cleaner welding technology. The process gas systems typically include an intricate array of tightly packed gas lines and valves which must be welded together. Very often, gas system welding is done in a clean room or like environment to reduce the incidence of particulate contaminants and an inert gas jet is used to reduce oxidation of molten stainless steel in the weld pool. The quantity of molten metal at the weld spot, and the environment at the weld zone created by the welder and the welding method itself are generally the greatest sources of gas panel weld contamination.
Automatic orbital head arc welding systems are known and used to weld stainless steel gas panels. The systems disclosed in U.S. Pat. Nos. 4,370,541 5,196,664 5,107,090 4,810,848 and 4,372,474 include a variety of features and weld head constructions. Arc welding systems generally produce high levels of heat which cause excessive melting and vaporization. Molten metal may trap particulates or oxidize and increase the incidence of contamination. Similarly, vaporization of corrosion resistant metal in the alloy being welded may lead to increased corrosion at the weld and possible contamination.
The '664 patent discloses a hinged clamp having an inert gas discharge to produce an increased purity weld by providing the gas in a stream which does not pass over particle-generating components such as gears. Though this may reduce the incidence of particles blown directly onto the weld, it does not eliminate generation of particles in the weld environment. Further, the gas jet may reduce, but does not eliminate oxidation of molten metal in the weld pool, does not limit vaporization of corrosion resistant alloys, and may even spatter the molten metal, if the pressure of the jet is raised in an attempt to improve weld purity, creating particulate contaminants.
The '541 patent discloses an envelope 7 which surrounds the weld zone and includes electron gun 13 within an enclosure 6 which is evacuated to limit weld pool oxidation. The welding element must be within the vacuum chamber so it can arc to the tube and affect the weld. As a consequence, the chamber must be large enough to include the entire weld head. This arrangement, therefore, can not readily be used for applications such as gas panels in which welds must be made in areas which often do not provide sufficient space to establish a surrounding vacuum chamber, and inherently limits weld purity since the weld zone includes moving parts which may generate particulate contaminants.
Laser welding is also well known in the prior art. U.S. Pat. Nos. 4,879,450 4,141,460 4,162,390 and German Patent Application No. 3620585 A1 disclose a variety of laser welding techniques for manufacturing a number of different products. The German application relates to laser welding a cold solder joint. The '042 patent relates to laser sealing vacuum insulated bottles. The '450 patent relates to welding pressure transducers, watch crystals or other parts wherein one part is permeable to a laser beam. The '460 patent relates to sealing light bulbs by melting an aperture blockade member. The '390 patent relates to using a gas stream and exhaust port for simultaneously cooling the light transmitter, deflecting ionized particles, and removing weld debris. None of the techniques appear to be directed to welding tubes in abutment in tight spaces, or to include a pressurized chamber for the purpose of obtaining high purity welds in tight spaces.
U.S. Pat. Nos. 4,080,525 4,429,211 and 4,533,814 disclose laser pipe welding apparatuses which include reflectors for aligning and focusing the beam. In the '814 device, the reflector is moved around the pipe by hinged arms. U.S. Pat. Nos. 4,578,554 4,564,736 4,673,795 4,963,714 and 4,906,812 disclose fiber optic laser welding devices having a variety of features. The '812 device mechanically engages and applies pressure to the workpiece. The '736 device is handheld and includes an inert gas jet. None of these devices apparently include a pressurized chamber, or appear particularly adapted to welding in tight spaces or producing clean, repeatable welds.
What is desired, therefore, is a laser welder that provides low heat input, clean welds in tight spaces such as a gas delivery panel.